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rXXXX American Chemical Society A dx.doi.org/10.1021/ic201053t | Inorg. Chem. XXXX, XXX, 000–000
ARTICLE
pubs.acs.org/IC
Modulation of Metal!Metal Separations in a Series of Ag(I)and Intensely Blue Photoluminescent Cu(I) NHC-BridgedTriangular ClustersVincent J. Catalano,* Lyndsay B. Munro, Christoph E. Strasser, and Ahmad F. Samin
Department of Chemistry, University of Nevada, Reno, Nevada 89557, United States
bS Supporting Information
’ INTRODUCTION
N-heterocyclic carbenes (NHCs) are excellent ligands fortransition metals, and ever since the isolation of the stable, freeNHC ligands by Arduengo and co-workers1 in 1991, NHCs havefound widespread application in transition-metal chemistry,particularly in catalysis.2!9 The NHC complexes of Ag(I) areincredibly simple to prepare and routinely employed as con-venient carbene-transfer reagents.5,10,11 Yet, on their own, Ag(I)NHC complexes are receiving increased attention because oftheir application as antimicrobial agents.2,5,12 In contrast, copper-(I) NHC complexes are much less prevalent in the literaturebut are starting to gain interest through their application incatalysis, for example, hydrosilylation,7 dipolar cycloaddition,and 8 C!N/O8,9 and C!C bond formation.3,4,9
Because of their excellent sigma-donating ability and the easewith which the precursors can be structurally modified withadditional functional groups, NHCs are also ideal ligands formaintaining multimetallic architectures, producing complexeswith short metal!metal interactions.5,9,11 These noncovalent,attractive (metallophilic) interactions are often responsiblefor luminescence frequently observed in compounds of thegroup 11 metals.13!17 While aurophilic attractions betweenAu(I) centers are the most well-studied,18!21 the metallophilic
interactions of the lighter coinage metals Cu and Ag remain lessexplored.22!25
In 2003, we reported the structure and luminescent propertiesof the NHC-bridged trimetallic complex, [Ag3(im(CH2py)2)3]-(BF4)3, containing a nearly equilateral Ag3
3+ triangular core withvery short Ag 3 3 3Ag separations ranging from 2.7598(8) to2.7765(8) Å (Scheme 1).26 Despite the Coulombic repulsionbetween the cationic Ag(I) centers, the observed intermetallicseparations are considerably shorter than the sum of the van derWaals radii and even shorter than the Ag 3 3 3Ag distance found inthe bulk metal (2.889 Å).27 Likewise, a similar Ag 3 3 3Ag separationwas found in the analogous 2-quinolyl-substituted NHC com-plex, [Ag3(im(CH2quin)2)3](BF4)3.
28 This triangular [Ag3L3]3+
arrangement appears to be a common structural motif in silver-NHC chemistry, and a number of other groups have reportedsimilar complexes. Youngs and co-workers29 found Ag 3 3 3Agseparations of 2.7869(6)!2.8070(5) Å in the hydroxymethyl-substituted complex, [Ag3(im(CH2py-6-CH2OH)2)3](NO3)3,whereas Lee30 and co-workers observed Ag 3 3 3Ag separationsranging from 2.8182(5) to 2.8312(5) Å in the closely related
Received: May 18, 2011
ABSTRACT: A series of picolyl-substituted NHC-bridged triangular complexes of Ag(I)and Cu(I) were synthesized upon reaction of the corresponding ligand precursors,[Him(CH2py)2]BF4 (1a), [Him(CH2py-3,4-(OMe)2)2]BF4 (1b), [Him(CH2py-3,5-Me2-4-OMe)2]BF4 (1c), [Him(CH2py-6-COOMe)2]BF4 (1d), and [HSim(CH2py)2]-BF4 (1e), with Ag2O and Cu2O, respectively. Complexes [Cu3(im(CH2py)2)3](BF4)3(2a), [Cu3(im(CH2py-3,4-(OMe)2)2)3](BF4)3 (2b), [Cu3(im(CH2py-3,5-Me2-4-OMe)2)3]-(BF4)3, (2c), [Ag3(im(CH2py-3,4-(OMe)2)2)3](BF4)3, (3b), [Ag3(im(CH2py-3,5-Me2-4-OMe)2)3](BF4)3 (3c), [Ag3(im(CH2py-6-COOMe)2)3](BF4)3 (3d), and [Ag3(
Sim-(CH2py)2)3](BF4)3 (3e) were easily prepared by this method. Complex 2e,[Cu3(
Sim(CH2py)2)3](BF4)3, was synthesized by a carbene-transfer reaction of 3e,[Ag3(
Sim(CH2py)2)3](BF4)3, with CuCl in acetonitrile. The ligand precursor 1d did notreact with Cu2O. All complexes were fully characterized by NMR, UV!vis, andluminescence spectroscopies and high-resolution mass spectrometry. Complexes2a!2c, 2e, and 3b!3e were additionally characterized by single-crystal X-ray diffraction. Each metal complex contains a nearlyequilateral triangular M3 core wrapped by three bridging NHC ligands. In 2a!2c and 2e, the Cu!Cu separations are short andrange from 2.4907 to 2.5150 Å. In the corresponding Ag(I) system, the metal!metal separations range from 2.7226 to 2.8624 Å.The Cu(I)-containing species are intensely blue photoluminescent at room temperature both in solution and in the solid state.Upon UV excitation in CH3CN, complexes 2a!2c and 2e emit at 459, 427, 429, and 441 nm, whereas in the solid state, these bandsmove to 433, 429, 432, and 440 nm, respectively. As demonstrated by 1H NMR spectroscopy, complexes 3b!3e are dynamic insolution and undergo a ligand dissociation process. Complexes 3b!3e are weakly photoemissive in the solid state.
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Inorganic Chemistry ARTICLE
methyl-substituted complex, [Ag3(im(CH2py-6-Me)2)3](PF6)3.Extending the NHC backbone, Chen and co-workers31 prepared thebenzimidazole-NHC-based triangular Ag3 complex, [Ag3(benzim-(CH2py)2)3](BF4)3, that contains very short Ag 3 3 3Ag separa-tions of only 2.777(1) Å. Finally, the triangular [Ag3L3]
3+motif isnot limited to symmetrically substituted NHC ligands. In 2005,we reported32 the structure of [Ag3(MeimCH2py)3(MeCN)2]-(BF4)3 (MeimCH2py = 1-methyl-3-[(2-pyridyl)methyl]imidazol-2-ylidene), which also contains a Ag3
3+ triangular core bridged bythe dissymmetric bidentate MeimCH2py ligand with Ag 3 3 3Agseparations ranging from 2.7598(8) to 2.7832(8) Å. Two of the threesilver centers are coordinated by additional acetonitrile molecules thatoccupy the remaining coordination sites resulting from the lack of asecond picolyl donor group on the NHC ligand. The role of ligandconstraint in these short separations can be discounted because theim(CH2py)2 ligand is capable of spanningmetal!metal separations aslong as 4.6 Å33 and as short as 2.49 Å, as demonstrated in this work.
The Cu(I) NHC chemistry is still relatively unexplored34
compared to that of Ag(I) even though the applicability of Cu(I)NHC molecules to catalysis has been demonstrated.3,4,7!9 Theanalogous NHC-bridged [Cu3L3]
3+ triangular complexes areconspicuously absent from the literature. Only recently, twoexamples of related copper complexes with less flexible linker-free1,3-bis(2-pyrimidinyl)imidazolylidene ligands have been reported.35
There are, however, reports of other structural motifs exhibitingshort intermetallic contacts between Cu(I) or Ag(I) with NHCligands bearing pyridyl functional groups. For example, tri- andtetranuclear copper and silver NHC complexes showing shortintermetallic distances are known for linear,36!39 butterfly, orrectangular37,40!42 arrangements of the metal atoms. There alsoexists an extensive body of literature on triangular d10 complexesbridged by anionic pyrazolate ligands;43!50 however, in thesecases, the metal!metal separations are typically greater than 3 Å.
In this Article, we present an extended study on NHC-bridgedtriangular complexes of Cu(I) and Ag(I) where we explore themodulation of the intermetallic distances by steric and electroniceffects and its implication on the luminescent behavior.
’RESULTS
As shown in Scheme 2, the imidazole-based NHC ligand pre-cursors 1b!1d were prepared analogously to the previouslyreported51 imidazolium salts, 1a, by simple alkylation of imidazole
with the respective (halomethyl)pyridine. The imidazolinylidene-based NHC precursor 1e was prepared analogously to literatureprocedures52,53 by first condensing 1,2-diaminoethane with pyri-dine-2-carboxaldehyde to form a Schiff base that was then reducedwith NaBH4. The resulting secondary amine was cyclized withtriethyl orthoformate in the presence of NH4BF4 to yield theimidazolinium salt.
According to Scheme 3, the triangular carbene compounds2a!2cwere conveniently prepared by stirring the respective ligand precursorwith an excess of Cu2O in refluxing acetonitrile. The correspondingsilver complexes, 3b!3d, were prepared at room temperatureanalogously to the preparation of 3a.26 Likewise, as shown inScheme 4, the saturated NHC precursor 1e [HSim(CH2py)2]BF4reacts smoothly at room temperature with excess Ag2O to form[Ag3(
Sim(CH2py)2)3](BF4)3, 3e. The corresponding reactionwith Cu2O failed, and [Cu3(
Sim(CH2py)2)3](BF4)3, 2e, couldonly be obtained through a transmetalation reaction54 of thesilver analog with CuCl. All attempts to prepare the Cu(I)triangular complex with the ester-containing ligand precursor1d failed. The direct reaction with Cu2O did not produce anymetalated product, and the transmetalation of 3d with copperhalide yielded only impure, multimetallic mixtures.
All of these metal complexes dissolve readily in commonorganic solvents, including acetonitrile, acetone, and dichloro-methane, except for 2c and 3c, which are nearly insoluble inchlorocarbons. The copper compounds are air-stable in solutionand in the solid state. The analogous silver compounds do notnoticeably decompose when protected from ambient light.
Scheme 1 Scheme 2
Scheme 3
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Crystals suitable for single-crystal X-ray diffraction wereobtained for complexes 2a!2c, 2e, and 3b!3e. Crystals of2b 3 6.5CH3CN grown from acetonitrile and diethyl ether con-tained significant solvent disorder and yielded poor data. Itsstructure is provided in the Supporting Information (Figure S3).Better quality crystals were obtained by slow vapor diffusion ofEt2O into propionitrile solutions of 2b. Crystallographic detailsare listed in Table 1. Comparative views of the cationic portionsof the copper-containing species 2a!2c and 2e are presented inFigure 1, while complete thermal ellipsoid plots and bonddistances and angles are provided in the Supporting Information.Selected bond distances and angles for 2a and 2b are listed inTable 2, whereas distance and angle data for 2c and 2e areprovided in Tables 3 and 4, respectively.
As seen in Figure 1, the copper-containing cations are nearlyD3 symmetric with a triangular Cu3 core wrapped by three NHCligands. Each Cu(I) center is coordinated by two pyridyl groupsand two bridging NHC moieties from alternating ligands. Themethylene linkages of the same NHC ligand are positioned toopposite faces of the Cu3 core. Both 2a and 2b crystallize in themonoclinic space group P21/c each with a complete cation in theasymmetric unit, whereas complex 2c crystallizes in the mono-clinic space group C2/c with only one-half of the cation in theasymmetric unit. The remaining atoms of the cation are relatedby a crystallographic 2-fold rotation. Complex 2e crystallizes inthe trigonal space group R3, and only one-third of the complex iscrystallographically unique with the remaining atoms related by3-fold symmetry.
The metal!metal separations in 2a!2c and 2e are verysimilar and remarkably short. As shown in Table 2, the Cu!Cuseparations range from 2.5088(8) to 2.5143(7) Å for theunsubstituted pyridyl complex, 2a, and these distances are quitesimilar to the values (2.5014(5)!2.5150(5) Å) in the di-methoxy-substituted pyridyl-containing complex, 2b. The short-est separations, albeit not by much, are found in the mixeddimethylmethoxy!pyridyl-substituted complex, 2c, where theCu1!Cu2 and Cu2!Cu2A distances measure only 2.4907(10)and 2.5054(12) Å. Saturating the imidazole backbone has verylittle effect on the Cu!Cu distances, and metal!metal separa-tion measures 2.4929(7) Å in the highly symmetric complex, 2e.Likewise, there is little variance in the Cu!C and Cu!Nseparations in 2a!2c and 2e; however, the average Cu!Ndistances do roughly track the trend in metal!metal separations. T
able1.
X-ray
CrystallographicDatafor2a!2c,2e,and3b!3e
compound
2a30.5CH3C
N2b
33C2H
5CN
2c33CH2C
l 22e
33CH3C
N3b
34C2H
5CN3C
4H10O
3c3C
2H5C
N3C
4H10O
3d3CH3C
N3e
34CH3C
N
form
ula
C45H42Cu 3N7B
3F123
0.5C
2H3N
C57H66Cu 3N12O12B 3F 1
23
3C3H
5N
C63H78Cu 3N12O6B
3F123
3CH2C
l 2
C45H48Cu 3N12B 3F 1
23
3C2H
3N
C57H66Ag 3N12O12B 3F 1
23
4C2H
3N3C
4H10O
C63H78Ag 3N12O6B
3F123
C3H
5N3C
4H10O
C57H54Ag 3N12O12B 3F 1
23
C2H
3N
C45H48Ag 3N12B 3F 1
23
4C2H
3N
fw1222.5
1727.5
1805.2
1331.2
1933.6
1812.6
1724.2
1505.2
crystalsize,mm
0.02
"0.02
"0.02
0.23
"0.12
"0.04
0.22
"0.05
"0.02
0.15
"0.04
"0.02
0.10
"0.05
"0.04
0.18
"0.17
"0.03
0.22
"0.03
"0.03
0.15
"0.12
"0.04
crystalsystem
monoclinic
monoclinic
monoclinic
trigonal
monoclinic
trigonal
trigonal
trigonal
spacegroup
P21/c
P21/c
C2/c
R3P2
1/c
P31
P-31c
P31c
a,Å
11.5777(5)
12.0260(1)
13.1899(7)
12.9314(2)
28.9522(5)
12.5762(1)
13.4196(3)
13.0585(3)
b,Å
35.4318(15)
26.5274(3)
20.8644(11)
12.9314(2)
13.0597(2)
12.5762(1)
13.4196(3)
13.0585(3)
c,Å
12.3604(6)
24.3308(2)
28.1272(16)
31.0630(6)
22.8804(4)
42.7806(4)
19.9460(5)
21.1922(5)
β,!
91.321(4)!
99.161(1)!
100.510(2)
110.102(1)
V,Å
35069.1(4)
7662.97(12)
7610.7(7)
4498.47(13)
8124.2(2)
5859.71(9)
3110.75(13)
3129.63(13)
Z4
44
34
32
2
F,Mg3m
!3
1.602
1.497
1.575
1.474
1.581
1.541
1.841
1.597
μ,mm!1
1.340
0.922
1.129
1.140
0.813
0.833
1.046
1.015
R 1[I>2σ
(I)]
0.0509
0.0548
0.0682
0.0531
0.0532
0.0379
0.0564
0.0373
wR 2
(alldata)
0.1136
0.1712
0.2100
0.1632
0.1343
0.0740
0.1359
0.1154
Scheme 4
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Inorganic Chemistry ARTICLE
The shortest Cu!Nave at 2.141 Å is found in 2c, followed veryclosely by 2b where Cu!Nave is 2.143 Å. The two complexeswithout auxiliary pyridyl-substitutions (2a and 2e) have similar,yet slightly longer, Cu!Nave separations of 2.155 and 2.151 Å,respectively. The Cu3 cores of 2a!2c possess nearly equilateralangles close to 60!, whereas in 2e, the core is crystallographicallyrestrained to an equilateral triangle. In all of the copper-contain-ing complexes, the Npy!Cu!Npy angles, which range from 91 to98!, are more reflective of a cis coordination mode, while theCcarbene!Cu!Ccarbene angles are distorted from linearity andrange from 162.2(1)! to 164.8(1)!.
Crystallographic data for the Ag(I)-containing triangularspecies, 3b!3e, are presented in Table 1. Both 3b and 3ccrystallize with one complete cation in the asymmetric unit,whereas 3d and 3e possess 3-fold symmetry and crystallize withonly one-third of the cation in the asymmetric unit. Structuraldiagrams of 3b!3e are presented in Figure 2, while completethermal ellipsoid plots and bond distances and angles arepresented in the Supporting Information. Selected bond dis-tances for 3b and 3c are presented in Table 5, whereas Tables 6and 7 list selected distances and angles for 3d and 3e, respec-tively. Like their copper congeners, the cations of 3b!3e allcontain equilateral (or nearly equilateral) Ag3 cores wrapped bythree NHC ligands. The bridging carbene moieties position
themselves nearly perpendicularly to the trimetallic face, forcingthe pendant picolyl groups to either side of the Ag3 core. Like itscopper counterpart, the shortest Ag!Ag separation is found inthe dimethylmethoxy!pyridyl-substituted complex, 3c, whereAg1!Ag2, Ag1!Ag3, and Ag2!Ag3 measure only 2.7634(3),2.7276(3), and 2.7226(3) Å, respectively. These values are veryclose to those found in the saturated backbone complex, 3e,where all three symmetry-related Ag!Ag distances measure only2.7292(5) Å. Not surprisingly, the longest Ag!Ag separation ismeasured in the ester containing complex, 3d, where thissubstitution in the 6-position of the pyridyl group causessignificant congestion around these aryl groups. The carbonylmoiety of the ester group is directed toward the nitrogen atom ofthe adjacent pyridyl ring with an O!N separation of !3.1 Å.Figure 3 presents a larger view of this steric congestion. In thedimethoxy-substituted pyridyl complex 3b, the Ag!Ag separa-tions of 2.7471(6), 2.7568(6), and 2.7584(6) Å for Ag1!Ag2,Ag2!Ag3, and Ag1!Ag3, respectively, although longer thanthose found in 3c, are still quite short. The average Ag!Nseparations roughly track the trend observed in the Ag!Agdistances. In the series, complexes 3c and 3e have nearly equalAg!Nave separations of 2.37 and 2.36 Å, respectively, consistentwith their shorter Ag!Ag distances. The longest Ag!N distanceof 2.685(4) Å is found in the ester-containing species 3d where
Figure 1. X-ray crystallographic drawings of the cationic portions of 2a!2c and 2e. All but the metal atoms are represented as small spheres. Hydrogenatoms are not shown for clarity. Complete thermal ellipsoid drawings and bond distances and angles are presented in the Supporting Information(Figures S1!S5).
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the carbonyl!pyridyl repulsion prevents closer approach of thenitrogen-containing moiety (Figure 3). The intermediate with aAg!Nave separation of 2.40 Å is 3b.
In CD3CN solution, the 1H NMR spectra (SupportingInformation) of the copper-containing species are consistentwith their solid-state structures. The approximateD3 symmetry isreflected in the diastereotopic methylene linkages that appear asAB quartets between 4.35 and 5.28 ppm for 2a!2c. In 2e, thesemethylene linker resonances are shifted upfield to 4.27 and 3.92ppm and are joined by an AA0BB0 pattern at 3.76 and 3.55ppm assigned to the backbone protons of the imidazolinylideneNHC ligand. The pyridyl protons in 2a were assigned based onits 2D-ROESY, gCOSY, and gHSQC spectra, and notably, thesignal of the H6 of the pyridyl ring appears at 6.585 ppm, which isunusually shielded by 1.96 ppm relative to its ligand precursor.This diamagnetic anisotropy55 stems from the orientation of thisproton and its close proximity (2.9 Å) to the centroid of theNHC imidazole ring.56,57 Saturating the imidazole removes thearomaticity, and hence the “ring current”, and forces the H6
signal in 2e back downfield to 7.82 ppm even though the distancebetween the proton and the centroid of the imidazolinylideneremains short at !3.0 Å. In the dimethylmethoxy-substitutedpyridyl complex 2c, the H6 resonance is easily identified as asinglet that appears at 6.23 ppm, whereas the corresponding
proton in 2b resonates at 6.28 ppm. Both of these complexeshave short proton!NHCcentroid separations ranging from 2.8 to3.0 Å.
At room temperature, all of the triangular Ag3 compounds arefluxional. As shown in Figure S19 (Supporting Information), inCD3CN at 25 !C, the methylene protons in the dimethoxy-substituted 3b appear as two broad resonances at 4.83 and 5.60ppm. In the dimethylmethoxy-substituted 3c, the correspondingresonances have coalesced to a very broad single peak at 5.12 ppm.The dynamic process in the ester-containing 3d is more facile,and at room temperature, themethylene protons are close to the fastexchange limit, appearing as a sharp singlet 5.44 ppm. Saturatingthe imidazole backbone as in 3e retards this process, but thecomplex is still fluxional with four broad resonances appearing at4.57, 4.22, 3.89, and 3.62 ppm associated with the four methylenegroups. This dynamic behavior is consistent with the pyridyldissociation mechanism as is the observation that the stericallyencumbered 3d exhibits the most facile exchange. Furthermore,mixing samples of 3c and 3e leads to rapid ligand exchange, asevidenced by the increased number of resonances observed in the1H NMR spectrum. In contrast, mixing 2c and 2e results only inthe superposition of the two spectra, indicating that there is noexchange. Likewise, addition of [Cu(NCCH3)4]BF4 to an NMR
Table 2. Selected Bond Lengths (Å) and Angles (!) for 2aand 2b
2a 2b
Cu1!Cu2 2.5088(8) 2.5014(5)
Cu2!Cu3 2.5143(7) 2.5150(5)
Cu1!Cu3 2.5089(8) 2.5055(5)
C1!Cu1 2.040(4) 2.051(3)
C1!Cu2 2.030(5) 2.014(3)
C16!Cu2 2.044(5) 2.007(3)
C16!Cu3 2.026(5) 2.042(3)
C31!Cu1 2.044(4) 2.056(3)
C31!Cu3 2.033(5) 2.039(3)
Cu1!N3 2.165(4) 2.132(3)
Cu1!N12 2.128(4) 2.139(2)
Cu2!N4 2.189(4) 2.134(3)
Cu2!N7 2.146(4) 2.158(2)
Cu3!N8 2.130(4) 2.153(3)
Cu3!N11 2.171(4) 2.143(2)
Cu1!Cu2!Cu3 59.93(2) 59.928(13)
Cu2!Cu1!Cu3 60.14(2) 60.306(14)
Cu1!Cu3!Cu2 59.93(2) 59.765(13)
Cu1!C1!Cu2 76.12(16) 75.96(10)
Cu2!C16!Cu3 76.31(17) 76.8(1)
Cu1!C31!Cu3 75.96(15) 75.44(10)
N3!Cu1!N12 91.73(15) 96.08(10)
N4!Cu2!N7 94.31(15) 92.13(10)
N8!Cu3!N11 93.36(15) 97.53(10)
C1!Cu1!C31 163.70(19) 163.45(11)
C1!Cu2!C16 163.36(18) 164.56(11)
C16!Cu3!C31 164.28(18) 162.22(11)
C4!N1!N2!C10 !34.5 27.2
C19!N5!N6!C25 !41.7 21.5
C34!N10!N9!C40 !40.5 32.1
Table 4. Selected Bond Lengths (Å) and Angles (!) for 2ea
Cu1!Cu1A 2.4929(7)
Cu1!C1 2.042(4)
Cu1!C1A 2.044(4)
Cu1!N3 2.153(4)
Cu1!N4A 2.148(4)
Cu1!Cu1A!Cu1B 60.0
Cu1!C1!Cu1A 75.20(13)
N3!Cu1!N4A 93.28(13)
C1!Cu1!C1A 164.80(13)
C4!N1!N2!C10 67.6a Symmetry operator for atoms labeled A and B: (A)!y + 1, x! y + 1;(B) !x + y, !x + 1, z.
Table 3. Selected Bond Lengths (Å) and Angles (!) for 2ca
Cu1!Cu2 2.4907(10)
Cu2!Cu2A 2.5054(12)
Cu1!C1 2.032(6)
Cu2!C16 2.029(6)
Cu2!C1 2.026(5)
Cu1!N3 2.129(5)
Cu2!N4 2.154(5)
Cu2!N7 2.139(5)
Cu1!Cu2!Cu2A 59.806(18)
Cu2!Cu1!Cu2A 60.39(4)
Cu1!C1!Cu2A 75.74(19)
Cu2!C16!Cu2A 76.2(3)
N3!Cu1!N3A 93.3(3)
N4!Cu2!N7 95.16(18)
C1!Cu1!C1A 164.4(3)
C1!Cu2!C16 163.7(2)
C10!N1!N2!C4 12.2
C18!N5!N5A!C18A 16.5a Symmetry operator for atoms labeled A: !x, y, !z + 1/2.
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Inorganic Chemistry ARTICLE
sample of 3b nearly instantaneously generates a spectrum con-sistent with a mixture of Cu- and Ag-containing species.
Variable-temperature NMR data are presented in the Sup-porting Information (Figures S20, S24, S30), and portions of theVT NMR spectra (d6-acetone) for 3e and the room-temperaturespectrum of 2e are shown in Figure 4. The poor solubility ofcomplexes 3b!3e made it difficult to find a single solvent inwhich the complexes remain soluble at low temperature whilespanning a wide enough temperature range to capture the entiredynamic process. In all cases, the stopped exchange limitexceeded the experimental conditions. Switching from d3-acet-onitrile to d6-acetone appears to slow the dynamic process. Forexample, in d6-acetone at 25 !C, the methylene resonances of 3bnow appear as a broad AB quartet that coalesces into two broadsinglets near 50 !C, but this temperature is still below the fastexchange limit. Lowering the temperature regenerates the ABquartet and shifts the two pyridyl resonances downfield to 7.13and 7.19 ppm and the NHC backbone proton to 7.95 ppm.At !85 !C, the complex starts to precipitate. A similar trend isobserved for 3c, but the process is more facile. In d6-acetone at25 !C, the methylene protons appear as two broad, unresolved
resonances that split into an AB quartet at !15 !C. A similartrend is observed for the saturated ligand species 3e (d6-acetone)where the stopped exchange limit again exceeds the experimentalconditions, but a clear pattern similar to that of 2e is observedat !60 !C. Heating this sample to 50 !C significantly broadensthe four methylene resonances but does not bring it to the fastexchange limit. The ester-containing species, 3d, has poorsolubility in acetone. In CD3CN at !40 !C, the sharp singletobserved at room temperature corresponding to the fast ex-change of the methylene protons only broadens slightly, indicat-ing only slight diminution of the dynamic process.
The 13C{1H} spectra of 2a!2c, 2e, and 3b!3e show theexpected signals at shifts comparable to the ligand precursors,except for the NHC carbon signals, which are not observed in theroutine 1D spectra. Only by performing gHMBC experimentscould the carbene shift be determined; crosspeaks with thecarbene were observed for both the CH2 linker groups and H4/5
of the NHC. For the silver compounds 3b and 3c, additional 1JAgCcoupling constants of 96(1) and 97(2) Hz, respectively, wereobserved. The resolution of the 2D spectrum did not allowfurther analysis into 107Ag and 109Ag contributions or detection of
Figure 2. X-ray crystallographic drawings of the cationic portions of 3b!3e. All but the metal atoms are represented as small spheres. Hydrogen atomsare not shown for clarity. Complete thermal ellipsoid drawings and bond distances and angles are presented in the Supporting Information (FiguresS6!S9).
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additional splitting by the remaining silver nucleus not bridged bythe NHC. Similar experiments for 3d and 3e did not reveal theAg!C coupling.
All of the compounds were further characterized by high-resolution electrospray mass spectrometry (Figures S42!S48,Supporting Information). With the exception of 3d, the multi-metallic assemblies remain intact in the gas phase where peakswith the proper isotopomer patterns corresponding to{[M3L3](BF4)2}
+ are observed. For 3d, only peaks correspond-ing to ligand precursor (1d) were observed.
In acetonitrile, the electronic absorption spectra of the ligandprecursors 1a!1e each show a single sharp band between 253and 265 nm associated with the pyridyl π!π* transition. All butthe ester-containing ligand precursor (1d) also show additionalweak shoulders at !294 nm. These features are generallyretained in the Cu3-containing species along with additionalpeaks at 374, 366, and 373 nm for 2a, 2b, and 2c, respectively. Inthe saturated ligand system, 2e, this band appears blue shifted to338 nm. As shown in Figure 5, the copper-containing triangles2a!2c and 2e exhibit very intense, blue photoluminescence insolution. The trend in emission maxima roughly follows theirsubstitution pattern. At room-temperature (CH3CN), the di-methoxy-substituted 2b and dimethylmethoxy-substituted 2chave the most blue shifted emission maxima at 427 and429 nm, respectively, followed by the saturated imidazole-con-taining complex 2e, which emits at 441 nm under UV excitation.At 459 nm, the emission of the unsubstituted species, 2a, is
the most red shifted. The excitation spectra (Supporting In-formation) for 2a!2c show that these emission bands areeffectively populated by two states. Changing the solvent has anegligible effect on the emission maxima, and 2b shows nomeasurable change in emission maximum or peak shape inchloroform, dichloromethane, acetone, or acetonitrile. However,in the solid state, the emission maxima of 2a shifts markedly to433 nm, whereas only small shifts in the emission maxima areobserved for 2b, 2c, and 2e, which now emit at 429, 432, and440 nm, respectively. The silver-containing triangles 3b!3e aremuch less emissive and less well-behaved. As evidenced by theirdynamic NMR spectroscopic behavior, complexes 3b!3e dis-sociate in acetonitrile solution, and their corresponding lumines-cence spectroscopy is unreliable. In the solid state, onlycomplexes 3c and 3e yielded reliable data with emission maximaat 425 and 424 nm, respectively. The emission spectra for solidsamples of complexes 3b and 3d are similar with broad weakemission bands centered at !410 nm.
’DISCUSSION
This work and the recent reports from the groups of Youngs,29
Lee,30 and Chen31 and our group clearly demonstrate thatpicolyl-substituted NHC molecules are excellent ligands forstabilizing the triangular [Ag3L3]
3+ structural motif and thatsubtle substitutions in ligand design can lead to significantvariation in Ag!Ag separation. For example, the silver triangle,[Ag3(im(CH2py)2)3](BF4)3, derived from the unsubstitutedpicolyl NHC ligand contains Ag(I) 3 3 3Ag(I) separations ranging
Table 5. Selected Bond Lengths (Å) and Angles (!) for 3band 3c
3b 3c
Ag1!Ag2 2.7471(6) 2.7634(3)
Ag2!Ag3 2.7568(6) 2.7226(3)
Ag1!Ag3 2.7584(6) 2.7276(3)
C1!Ag1 2.224(6) 2.261(3)
C1!Ag2 2.244(5) 2.218(3)
C16!Ag2 2.234(5) 2.202(3)
C16!Ag3 2.255(5) 2.261(3)
C31!Ag1 2.242(6) 2.282(3)
C31!Ag3 2.242(5) 2.277(3)
Ag1!N3 2.405(4) 2.365(3)
Ag1!N12 2.381(5) 2.352(3)
Ag2!N4 2.382(5) 2.347(3)
Ag2!N7 2.427(4) 2.436(3)
Ag3!N8 2.386(5) 2.375(3)
Ag3!N11 2.418(4) 2.360(3)
Ag1!Ag2!Ag3 60.154(15) 59.624(8)
Ag2!Ag1!Ag3 60.098(15) 59.446(8)
Ag1!Ag3!Ag2 59.748(15) 60.931(8)
Ag1!C1!Ag2 75.88(18) 76.18(9)
Ag2!C16!Ag3 75.78(18) 75.19(10)
Ag1!C31!Ag3 75.91(18) 73.48(10)
N3!Ag1!N12 99.25(15) 109.38(9)
N4!Ag2!N7 102.09(16) 100.54(9)
N8!Ag3!N11 103.95(15) 98.51(10)
C4!N1!N2!C10 !18.4 !1.9
C19!N6!N5!C25 !25.1 2.1
C34!N9!N10!C40 !28.1 0.0
Table 7. Selected Bond Lengths (Å) and Angles (!) for 3ea
3e
Ag1!Ag1A 2.7292(5)
C1!Ag1 2.241(6)
C1!Ag1B 2.236(6)
Ag1!N3 2.358(6)
Ag1!N4A 2.372(6)
Ag1A!Ag1!Ag1B 60.0
Ag1!C1!Ag1A 75.11(19)
N3!Ag1!N4B 95.26(18)
C10!N1!N2!C4 64.4a Symmetry operator for atoms labeled A and B: (A) !x + y, !x, z;(B): !y, x ! y, z.
Table 6. Selected Bond Lengths (Å) and Angles (!) for 3da
3d
Ag1!Ag1A 2.8624(9)
C1!Ag1 2.240(5)
C1!Ag1A 2.240(5)
Ag1!N3 2.685(4)
Ag1!N3B 2.685(4)
Ag1A!Ag1!Ag1B 60.0
Ag1!C1!Ag1B 79.4(2)
N3!Ag1!N32A 75.72(10)
C3!N1!N1C!C3C !11.7a Symmetry operator for atoms labeled A!C: (A)!x + y,!x, z; (B) x, x! y, !z + 1/2; and (C) !y, !x, !z + 1/2.
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from 2.7598(8) to 2.7765(8) Å.26 Incorporation of a methylgroup into the 6-position on the pyridyl group introduces somesteric encumbrance at the pyridyl centers, preventing their closeapproach to the Ag center, as evidenced by the relatively long(>2.5 Å) Ag!N separation. As a consequence, the Ag 3 3 3Agseparations lengthen to 2.8182(5)!2.8312(5) Å.30 Youngs andco-workers noted a similar trend in the 6-hydroxymethyl-pyridyl-substituted NHC complex [Ag3(im(CH2py-6-CH2OH)2)3]-(NO3)3 where the Ag 3 3 3Ag separations are similarly lengthened
and range from 2.7869(6) to 2.8070(5) Å].29 This substitution istaken to an extreme in 3d where the incorporation of a methylester group adds significant steric repulsion between the carbonyland pyridyl groups. The longer Ag 3 3 3Ag separations of2.8624(9) Å are consistent with very long Ag!Npy separationsof 2.685(4) Å. This weak ligand attachment is also manifested inVTNMR spectroscopy where the stopped exchange limit eludeddetection. Such long Ag!N interactions are not frequentlyencountered in the literature, but a few exist. For example,comparable distances were found in a butterfly-shaped tetrame-tallic cluster41 with a 1-[(1,8-naphthyridin-2-yl)methyl]-3-[(2-pyridyl)methyl]imidazolylidene (Ag!N up to 2.656 Å) and inthe [tris-(2-methylphenyl)phosphine]{bis[(2-pyridyl)methyl]-amine}silver cations where the longest Ag!N distances measure2.618 and 2.659 Å.58,59
The shorter Ag 3 3 3Ag separations found in 3b and 3c rangingfrom!2.72 to 2.76 Å are consistent with the addition of electron-donating groups onto the pyridyl rings, though the effect is not asdramatic as the differences seen by incorporating stericallyencumbering groups. Saturated imidazole NHC ligands are notsignificantly better sigma donors than their unsaturatedcounterparts,60 and therefore, the short Ag 3 3 3Ag separation of2.7292(5) Å measured in 3e likely originates from geometricconsiderations rather than electronic.61 The Sim(CH2py)2 ligandis less rigid and allows for increased flexibility of pendant picolylside arms. This is manifested in the increased CH2!N!N!CH2torsion angle of 64! in the Sim(CH2py)2-containing complexcompared to 30!34! for the same measurement in the unsatu-rated analog, [Ag3(im(CH2py)2)3](BF4)3.
26
To the best of our knowledge, complexes 2a!2c and 2e arethe first triangular NHC-bridged [Cu3L3]
3+ complexes withflexible pendant arms reported. Unlike their Ag(I) congeners,these complexes are robust and substitution-inert, making them
Figure 3. X-raycrystallographic representationof the steric repulsionbetweenthemethyl ester and pyridyl groups in the crystal structure of 3d 3MeCN.Oneligand is shown as transparent spheres with van der Waals radii.
Figure 4. Part A: subset of the variable-temperature NMR spectra forthe methylene region of [Ag3(
Sim(CH2py)2)3](BF4)3 (3e) in d6-acetone. Part B: room-temperature NMR data for the methylene regionof [Cu3(
Sim(CH2py)2)3](BF4)3 (2e) in d3-acetonitrile.
Figure 5. Normalized room-temperature emission spectra (CH3CN)for 2a!2c and 2e.
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ideal molecules for continued investigation. Complexes 2a!2care air stable and easily prepared by the simple reaction of Cu2Owith the appropriate ligand precursor. The similarly stablecomplex 2e with its saturated ligand backbone could only beprepared through a transmetalation reaction with 3e and cuproushalide. The inability to prepare the ester-containing Cu3 complexwith the ligand precursor 1d is not unexpected given that thesmaller triangular Cu3 core relative to the Ag3 analog wouldinduce increased congestion around the Cu(I) centers, prevent-ing adequate pyridyl coordination. Triangular Cu3 complexes areabundant in the literature; however, a search of the CambridgeCrystallographic Data Centre found only a modest number ofCu3-containing complexes with Cu!Cu separations shorter than2.6 Å. Most relevant is the closely related [Cu3(impy2)3]
3+
complex very recently prepared by Chen and co-workers62
through a novel electrochemical procedure. Here, the Cu!Cuseparations are similarly short and range from 2.465(1) to2.497(1) Å. None of the remaining entries in the CCDC is ahomoleptic complex with neutral ligands, making the shortCu 3 3 3Cu separations of !2.5 Å found in 2a!2c and 2eparticularly noteworthy. For example, Floriani and co-workers63
reported very short Cu!Cu separations ranging from 2.44 to2.60 Å in the mesityl-bridged Cu4(Mes)4(SC4H8)2 complex.Subsequently, J!akle and co-workers64 reported a similar per-fluorophenyl-bridged Cu4 cluster with 2.43!2.47 Å Cu!Cuseparations. Slightly longer Cu!Cu separations of 2.519 Å werereported by Hawthorne and co-workers65 in their trinuclear“cupracarborane” complex. Yam and co-workers66!69 have ex-tensively explored phosphine-bridged Cu3 complexes that areface-capped by an acetylide ligand and found Cu!Cu separa-tions ranging from !2.45 to 3.27 Å. The Cu!Cu separationsmeasured in 2a!2c and 2e follow a similar trend observed in theanalogous Ag complexes where increased electron density at thepyridyl site results in a shorter Cu!Cu separation. The differ-ences in the separations are quite small, and the shortestseparations are found in the complex with the most electron-rich pyridyl substitution, 2c, followed very closely by thedimethoxy complex, 2b, then the saturated imidazole backbonecomplex, 2e. The longest separations at!2.51 Å are found in theunsubstituted species.
One of the most striking features of complexes 2a!2c and 2eis their intense, blue photoemission. Although the nature of theexcited state is yet undetermined, preliminary data point toward apredominantly metal cluster-centered process. The lack of anysolvent effect on the emission energy is in conflict with thegeneration of a polar excited state typical of metal-to-ligandcharge transfers; however, a delocalized and symmetrical charge-transfer process is possible. Unlike the extensively studiedpyrazolate-bridged Cu3 triangular complexes47!50 whose closeintermolecular metal!metal interactions allow for excimer for-mation, all of the complexes reported here have very long (>10 Å)intermolecular Cu 3 3 3Cu separations in the solid state. In theabsence of excited-state aggregation, the phosphorescent state ofthe isolated pyrazolate-bridged Cu3 complex was assigned to ametal cluster-centered charge-transfer process mixed with someligand-to-metal charge-transfer character.70 Lastly, given that theligand precursors are luminescent, an intraligand transitionperturbed by the metal centers71 is possible; however, the lackof a similar emission in the Ag3 complexes discounts thismechanism. Regardless of the mechanism, blue emitting orga-nometallic compounds are rare,72!75 and this property is a highlydesirable feature for efficient organometallic light-emitting
diodes (OLEDs).71,73,74,76!78 Consequently, we are currentlyexploring other substitutions that might influence the emissionproperties and give insight into the excited state along the factorsthat influence the material processing characteristics.
The difference in the dynamic nature of the Ag3- and Cu3-containing complexes is interesting. In the absence of stericcongestion in the 6-postion of the pyridyl group, this dynamicbehavior likely originates from the geometric differences in themetal core sizes. The smaller Cu3 cores induce less strain acrossthe ligand than their Ag3 counterparts. This is evidenced by thelonger intraligand Npy 3 3 3Npy separations by!0.4 Å in the silvercomplexes relative to the copper-containing species and by theslight expansion observed in the angles around the methylenelinkages in the corresponding Ag systems. The nature of thesubstituents in the 6-substituted pyridyl complexes is alsoimportant. In systems containing a Lewis basic heteroatom (e.g., COOMe, 3d; and CH2OH
29), only a singlet for the CH2protons indicating fast exchange is observed, suggesting thatcompetition for Ag coordination is possible. However, spectatorsubstituents (benzo28 and Me30) in these positions appear tofreeze the dynamic motion on the NMR time scale perhaps bybuttressing the ligands against each other, and sharp AB quartetsare observed despite the rather long Ag!N separations, indicat-ing a weaker pyridyl coordination. In the absence of substituents,as in [Ag3(im(CH2py)2)3](BF4)3,
26 3b, 3c, and 3e, the facileexchange process leads to single resonances. The compound[Ag3(benzim(CH2py)2)3](BF4)3
31 also shows a broad singlet,but this is likely due to the different coordination mode of theligand and hence a different exchange phenomenon. Silver NHCcomplexes are expected to exhibit JAgC coupling; however, suchsignal splitting is frequently not observed.5 Typical 1J107AgC and1J109AgC coupling constants for [Ag(NHC)2]
+ species rangefrom 180 to 189 Hz,79!82 and these values are larger than thoseobserved here. However, the bridging nature of the NHCobserved in the Ag3 triangular complexes would be expected todecrease the coupling constants. A 1J109AgC of 104.5 Hz wasmeasured for the unsubstituted [Ag3(im(CH2py)2)3](BF4)3complex,26 which is in good agreement with the values foundfor 3b and 3c.
’CONCLUSION
In this paper, we report the preparation of several new picolyl-substituted N-heterocyclic carbene precursors and their Cu(I)-and Ag(I)-containing triangular M3 complexes. These eightcomplexes add to the growing family of NHC-bridged triangularstructural motifs. Substitution away from the coordinationsphere subtly influences the short M!M separations, whereassubstitution at the 6-position of the pyridyl ring perturbs metalcoordination in the silver-containing species, which, in turn,reduces the dispersivity at the Ag(I) center, resulting in longerAg!Ag separations. Whereas the Ag(I) species are weaklyphotoluminescent at best, the Cu(I) congeners are intenselyblue emissive.
’EXPERIMENTAL SECTION
All chemicals were used as received. NHC precursors, 1a51 and 1e,52,53
and 2-(bromomethyl)-6-(methoxycarbonyl)pyridinium bromide83,84
were prepared from the literature procedures. NMR spectra weremeasured on a Varian V500 NMR System spectrometer at the indicatedfrequencies and were referenced relative to the residual solvent signal.Assignments were based upon interpretation of gCOSY, gHSQC, and
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gHMBC experiments. Deuterated solvents were deoxygenized by twofreeze!thawing cycles for measurement of the copper compounds.Fluorescence spectra were recorded on a Jobin Yvon Horiba Fluoro-Max-3 instrument. High-resolution ESI mass spectra were obtained on anAgilentTechnologies 6230TOF-MS employing electrospray ionization inpositive ion mode; required masses are calculated with 10B, 63Cu, and107Ag isotopes if not noted otherwise.Single-crystal X-ray diffraction was performed on a Bruker SMART
Apex CCD instrument at 100 K using graphite-monochromated Mo KRradiation; crystals were immersed in Paratone oil and mounted on glassfibers. Data were corrected for Lorentz and polarization effects using theSAINT program and corrected for absorption using SADABS.85,86 Thestructures were solved by direct methods or Patterson syntheses usingthe SHELXTL 6.10 software package.87
1,3-bis[(3,4-Dimethoxy-2-pyridyl)methyl]-1H-imidazoliumTetrafluoroborate ([Him(CH2py-3,4-(OMe)2)2]BF4 (1b)). Imi-dazole (0.587 g, 8.61 mmol), 2-(chloromethyl)-3,4-dimethoxypyridinehydrochloride (3.85 g, 17.2 mmol), and NaHCO3 (3.62 g, 43.0 mmol)were added to a 100 mL round-bottom flask, and 1-propanol (40 mL)was added. The solution was refluxed overnight, cooled, and thenfiltered through Celite. The filtrate was evaporated to yield a pink oil,which was then taken up in 150 mL of MeOH and treated with asaturated aqueous solution of NaBF4 (4.72 g, 5.44 mmol). The solutionwas evaporated to dryness, and the residue was taken up in CH2Cl2 andagain filtered through Celite. The volume of the obtained solution wasreduced, and a pink solid was precipitated with Et2O in 78% yield (3.94 g).1H NMR (499.8 MHz, CD3CN, 25 !C): δ 8.71 (m, 1H, H-2 im), 8.13(d, J = 5.5 Hz, 2H, H-6 py), 7.42 (d, J = 1.6 Hz, 2H, H-4/5 im), 7.03 (d,J = 5.5 Hz, 2H, H-5 py), 5.44 (s, 4H, CH2), 3.92 (s, 6H, OMe), 3.87 (s,6H, OMe). 13C NMR (125.7 MHz, CD3CN, 25 !C): δ 159.9 (C-4 py),147.0 (C-2 py), 146.9 (C-6 py), 144.4 (C-3 py), 137.9 (C-2 im), 124.0(C-4/5 im), 110.0 (C-5 py), 61.6 (OMe-3), 56.9 (OMe-4), 50.6 (CH2).MS (ESI+):m/z 371.1722 [(M! BF4)
+, 100%], C19H23N4O4+ requires
371.171382. UV (CH3CN) λmax, nm (ε): 267 (5100).1,3-bis[(4-Methoxy-3,5-dimethyl-2-pyridyl)methyl]-1H-imi-
dazolium Tetrafluoroborate ([Him(CH2py-3,5-Me2-4-OMe)2]-BF4 (1c)). The compound was prepared analogously to 1b utilizingimidazole (0.510 g, 7.30 mmol), 2-(chloromethyl)-4-methoxy-3,5-di-methylpyridine hydrochloride (3.26 g, 14.6 mmol), NaHCO3 (3.04 g,36.2 mmol), and 1-propanol (50 mL). Compound 1c was obtained as acolorless solid in 88% yield (2.95 g). 1H NMR (499.8 MHz, CD3CN,25 !C):δ 8.65 (s, 1H,H-2 im), 8.13 (s, 2H,H-6 py), 7.41 (d, J= 1.6Hz, 2H,H-4/5 im), 5.44 (s, 4H, CH2), 3.76 (s, 6H, OMe), 2.25 (s, 6H,Me), 2.23(s, 6H, Me). 13CNMR (125.7MHz, CD3CN, 25 !C): δ 165.3 (C-4 py),151.8 (C-2 py), 150.3 (C-6 py), 138.4 (C-2 im), 128.0 (C-3 py), 126.0(C-5 py), 124.1 (C-4/5 im), 61.9 (OMe), 52.7 (CH2), 13.5 (Me-5), 10.8(Me-3). MS (ESI+):m/z 367.2133 [(M! BF4)
+, 100%], C21H27N4O2+
requires 367.212853. UV (CH3CN) λmax, nm (ε): 262 (2900).1,3-bis{[(6-Methoxycarbonyl)-2-pyridyl]methyl}-1H-imi-
dazolium Tetrafluoroborate ([Him(CH2py-6-COOMe)2]BF4,(1d)). The compound was prepared analogously to 1b using 2--(bromomethyl)-6-(methoxycarbonyl)pyridine (3.84 g, 16.7 mmol),imidazole (0.625 g, 9.19 mmol), and NaHCO3 (8.00 g, 9.52 mmol) in100 mL of MeCN. 1H NMR (499.8 MHz, CD3CN, 25 !C): δ 8.96 (s, 1H,H-2 im), 8.06 (d, J = 7.7 Hz, 2H, H-3 py), 8.00 (t, J = 7.7 Hz, 2H, H-4 py),7.63 (d, J = 7.7 Hz, 2H, H-5 py), 7.56 (s, 2H, H-4/5 im), 5.57 (s, 4H, CH2),3.88 (s, 6H, OMe). 13C NMR (125.7 MHz, CD3CN, 25 !C): δ 165.9(COOMe), 154.3 (C-2 py), 149.1 (C-6 py), 140.0 (C-4 py), 138.3 (C-2im), 127.0 (C-3 py), 125.8 (C-5 py), 124.3 (C-4/5 im), 54.7 (CH2), 53.3(OMe). MS (ESI+):m/z 367.1403 [(M! BF4)
+, 100%], C19H19N4O4+
requires 367.140082. UV (CH3CN) λmax, nm (ε): 267 (6200).1,3-bis[(2-Pyridyl)methyl]imidazolinium Tetrafluoroborate
([HSim(CH2py)2]BF4, (1e)). The ligand was prepared from N,N0-bis-(2-pyridyl)ethane-1,2-diamine (1.00 g, 4.13 mmol), triethyl orthoformate
(0.610 g, 4.12 mmol), and NH4BF4 (0.671 g, 6.40 mmol), with a yield of1.27 g (91%) of a colorless powder. 1H NMR (499.8 MHz, CD3CN,25 !C): δ 8.68 (m, 2H, H-6 py), 8.33 (s, 1H, H-2 Sim), 8.23 (m, 2H, H-4py), 7.74 (m, 2H, H-3 py), 7.71 (m, 2H, H-5 py), 4.93 (s, 4H, pyCH2),3.92 (m, 4H, H-4/5 Sim). 13C NMR (125.7 MHz, CD3CN, 25 !C): δ161.1 (C-2 Sim), 151.4 (C-2 py), 147.3 (C-6 py), 143.6 (C-4 py), 126.5(C-3/5 py), 126.3 (C-5/3 py), 51.7 (CH2), 50.3 (C-4/5 Sim). MS(ESI+): m/z 253.1452 [(M ! BF4)
+, 100%], C15H17N4+ requires
253.144773. UV (CH3CN) λmax, nm (ε): 255 (8500).[Cu3(im(CH2py)2)3](BF4)3 (2a). Ligand precursor [Him(CH2py)2]-
BF4 (0.0412 g, 0.122 mmol) was refluxed with an excess of Cu2O(0.0819 g, 0.572 mmol) in MeCN (10 mL) overnight. The suspensionwas filtered through Celite and reduced in volume, and a colorlesspowder was precipitated with Et2O, affording 0.0441 g (90%) of acolorless solid. Crystals of 2a 3 0.5MeCN suitable for X-ray diffraction wereobtained by diffusion of Et2O vapor into a MeCN solution of 2a. 1HNMR (499.8 MHz, CD3CN, 25 !C): δ 7.95 (td, 3J = 7.7 Hz, 4J = 1.7 Hz,6H, H-4 py), 7.57 (m, 6H, H-3 py), 7.42 (s, 6H, H-4/5 im), 7.22 (m, 6H,H-5 py), 6.59 (m, 6H, H-6 py), 4.91 (d, 2J = 15.1Hz, 6H,HCH), 4.80 (d,2J = 15.1 Hz, 6H, HCH). 13C NMR (125.7 MHz, CD3CN, 25 !C): δ166.6 (CCu), 151.2 (C-2 py), 147.0 (C-6 py), 137.9 (C-4 py), 123.6 (C-5 py), 123.0 (C-4/5 im), 122.7 (C-3 py), 54.0 (CH2). MS (ESI+):m/z 1111.1672 [(M ! BF4)
+, 0.1%], C45H42B2Cu3F8N12+ requires
1111.166882. UV (CH3CN) λmax, nm (ε): 257 (120 000), 374 (25 000).[Cu3(im(CH2py-3,4-(OMe)2)2)3](BF4)3 (2b). The preparation
followed that of 2a. Ligand precursor [Him(CH2py-3,4-(OMe)2)2]BF4,1b, (0.159 g, 0.346 mmol) and Cu2O (0.249 g, 1.73 mmol) afforded0.128 g of 2b (71%) as a tan powder. Crystals of 2b 3 6.5MeCN and2b 3 3EtCN suitable for X-ray diffraction were obtained by diffusion ofEt2O vapor into MeCN or EtCN/CH2Cl2 solutions of 2b, respectively.1H NMR (499.8 MHz, CD3CN, 25 !C): δ 7.29 (s, 6H, H-4/5 im), 6.80(d, 6H, 3J = 6.0 Hz, H-5 py), 6.28 (d, 6H, 3J = 6.0 Hz, H-6 py), 5.28 (d,6H, 2J = 15.3 Hz,HCH), 4.43 (d, 6H, 2J = 15.3 Hz, HCH), 3.93 (s, 18H,OMe-4), 3.88 (s, 18H, OMe-3). 13C{1H} NMR (125.7 MHz, CD3CN,25 !C): δ 167.9 (CCu) 157.7 (C-4 py), 144.4 (C-2 py), 143.4 (C-6 py),140.8 (C-3 py), 122.3 (C-4/5 im), 107.7 (C-5 py), 60.8 (OMe-3), 56.2(OMe-4), 47.7 (CH2).MS (ESI+):m/z 1471.2937 [(M! BF4)
+, 0.1%],C57H66B2Cu3F8N12O12
+ requires 1471.293609. UV (CH3CN) λmax, nm(ε): 262 (98 000), 366 (25 000).[Cu3(im(CH2py-3,5-Me2-4-OMe)2)3](BF4)3 (2c). Compound
2c was prepared analogously to 2a using 1c (0.236 g, 0.519 mmol)and Cu2O (0.374 g, 1.92 mmol), with a yield of 0.184 g (70%) of acolorless powder. Crystals of 2c 3 3CH2Cl2 suitable for X-ray diffractionwere obtained by evaporation of a CH2Cl2 solution of 2c. 1H NMR(499.8 MHz, CD3CN, 25 !C): δ 7.35 (s, 6H, H-4/5 im), 6.23 (s, 6H,H-6 py), 4.99 (d, 6H, 2J = 15.6 Hz, HCH), 4.35 (d, 6H, 2J = 15.6 Hz,HCH), 3.80 (s, 18H, OMe), 2.29 (s, 18H, Me-3), 1.98 (s, 18H, Me-5).13C{1H} NMR (125.7 MHz, CD3CN, 25 !C): δ 167.7 (CCu), 162.8(C-4 py), 149.4 (C-6 py), 146.4 (C-2 py), 125.7 (C-5 py), 124.0 (C-3py), 122.3 (C-4/5 im), 59.9 (OCH3), 50.2 (CH2), 13.7 (Me-5), 11.2(Me-3). MS (ESI+): m/z 1459.4156 [(M ! BF4)
+, 0.5%], C63H78B2-Cu3F8N12O6
+ requires 1459.418021. UV (CH3CN) λmax, nm (ε): 260(48 000), 373 (8300).[Cu3(
Sim(CH2py)2)3](BF4)3 (2e). A 50 mL round-bottom flaskwas charged with 3e (0.161 g, 0.11 mmol) and CH3CN (30 mL). Asolution of CuCl (34 mg, 0.35 mmol) in CH3CN (10 mL) was addeddropwise, and the mixture was stirred for 30 min. The resulting suspensionwas filtered through Celite, the volume was reduced, and 0.111 g (79%)of a colorless solid with a bluish tint was precipitated with Et2O. Crystalsof 2e 3 3MeCN suitable for X-ray diffraction were obtained by diffusionof benzene vapor into a MeCN solution of 2e. 1H NMR (499.8 MHz,CD3CN, 25 !C):δ 7.97 (m, 6H, H-4 py), 7.82 (m, 6H, H-6 py), 7.43 (m,12H, H-3 and H-5 py), 4.27 (d, 6H, 2J = 15.5 Hz, py!HCH), 3.92 (d,6H, 2J = 15.5 Hz, py!HCH), 3.76 (m, 6H, H-4/5 Sim), 3.55 (m, 6H,
K dx.doi.org/10.1021/ic201053t |Inorg. Chem. XXXX, XXX, 000–000
Inorganic Chemistry ARTICLE
H-4/5 Sim). 13C{1H}NMR(125.7MHz, CD3CN, 25 !C):δ 151.9 (C-2py), 147.9 (C-6 py), 137.7 (C-4 py), 123.6 (C-5 py), 123.1 (C-3 py),53.3 (py!CH2), 50.2 (C-4/5
Sim). MS (ESI+): m/z 1117.2187 [(M !BF4)
+, 0.3%], C45H48B2Cu3F8N12+ requires 1117.213784. UV
(CH3CN) λmax, nm (ε): 254 (110 000), 338 (18 000).[Ag3(im(CH2py-3,4-(OMe)2)2)3](BF4)3 (3b). A round-bottom
flask was charged with 1b (0.176 g, 0.385 mmol), Ag2O (0.432 g, 2.18mmol), and 30 mL of MeCN. The suspension was protected from lightand stirred overnight at room temperature. Subsequent filtration throughCelite, reducing in volume, and precipitation with Et2O afforded 0.180 gof 3b (82%) as a tan powder. Crystals of 3b 3 4MeCN suitable for X-raydiffraction were obtained by diffusion of Et2O vapor into a MeCNsolution of 3b. 1H NMR (499.8 MHz, CD3CN, 25 !C): δ 7.47 (s, 6H,H-4/5 im), 6.92 (d, 6H, 3J = 5.8 Hz, H-6 py), 6.87 (d, 6H, 3J = 5.8 Hz,H-5 py), 5.60 (br s, HCH), 4.83 (br s, HCH), 3.92 (s, 18H, MeO-4),3.91 (s, 18H, MeO-3). 13C{1H}NMR (125.7 MHz, CD3CN, 25 !C): δ174.6 (t, 1JCAg = 96(1) Hz, CAg), 158.3 (C-4 py), 144.6 (C-6 py), 144.4(C-2 py), 141.9 (C-3 py), 123.7 (C-4/5 im), 108.0 (C-5 py), 61.1(OMe-3), 58.3 (OMe-4), 49.2 (CH2). MS (ESI+): m/z 1603.2084[(M ! BF4)
+, 1%], C57H66Ag3B2F8N12O12+ requires 1603.220155.
[Ag3(im(CH2py-3,5-Me2-4-OMe)2)3](BF4)3 (3c). The compoundwas prepared analogously to 3b using 1c (0.246 g, 5.41mmol) and Ag2O(0.623 g, 2.71 mmol), affording 0.183 g (60%) of a colorless powder.Crystals of 3c 3 EtCN 3 Et2O suitable for X-ray diffraction were obtainedby vapor diffusion of Et2O in an EtCN/CH2Cl2 solution of 3c.
1HNMR(499.8 MHz, CD3CN, 25 !C): δ 7.53 (s, 6H, H-4/5 im), 6.84 (s, 6H,H-6 py), 5.12 (br m, CH2), 3.79 (s, 18H, OMe), 2.38 (s, 18H, Me-5),2.03 (s, 18H, Me-3). 13C{1H} NMR (125.7 MHz, CD3CN, 25 !C): δ173.1 (t, 1JCAg = 97(2) Hz, CAg), 163.3 (C-4 py), 149.4 (C-2 py), 147.7(C-6 py), 126.1 (C-5 py), 125.0 (C-3 py), 123.6 (C-4/5 im),60.0 (OMe), 52.1 (CH2), 13.5 (Me-3), 11.5 (Me-5). MS (ESI+):m/z 1591.3371 [(M ! BF4)
+, 0.1%], C63H78Ag3B2F8N12O6+ requires
1591.344570.[Ag3(im(CH2py-6-COOMe)2)3](BF4)3 (3d). The compound was
prepared analogously to 3b using 1d (0.231 g, 0.508 mmol) and Ag2O(0.588 g, 2.54 mmol), affording 0.146 g (51%) of a tan powder. Crystalsof 3d 3MeCN suitable for X-ray diffraction were obtained by diffusion ofEt2O vapor into a MeCN solution of 3d. 1H NMR (499.8 MHz,CD3CN, 25 !C): δ 7.97 (m, 6H, H-5 py), 7.90 (m, 6H, H-4 py), 7.45(m, 6H, H-3 py), 7.33 (s, 6H, H-4/5 im), 5.44 (s, 12H, CH2), 3.81 (s,18H, OMe). 13C{1H} NMR (125.7 MHz, CD3CN, 25 !C): δ 178.9(CAg), 162.8 (COOMe), 154.0 (C-2 py), 145.4 (C-6 py), 137.4 (C-4py), 124.6 (C-3 py), 123.2 (C-5 py), 121.5 (C-4/5 im), 56.2 (CH2), 52.5(OMe).[Ag3(
Sim(CH2py)2)3](BF4)3 (3e). The compound was preparedanalogously to 3b using 1e (0.30 g, 0.88 mmol) and Ag2O (1.02 g, 4.41mmol), affording 0.25 g (63%) of a colorless powder. Crystals of3e 3 4MeCN suitable for X-ray diffraction were obtained by diffusionof Et2O vapor into a MeCN solution of 3e. 1H NMR (499.8 MHz,CD3CN, 25 !C): δ 8.12 (m, 6H, H-6 py), 7.97 (td, 6H, 3J = 7.7 Hz, 4J =1.7 Hz, H-4 py), 7.49 (m, 6H, H-3 py), 7.44 (m, 6H, H-5 py), 4.57 (m,6H, py!HCH), 4.22 (m, 6H, py!HCH), 3.89 (m, 6H, N!HCH), 3.62(m, 6H, N!HCH). 13C{1H} NMR (125.7 MHz, CD3CN, 25 !C):δ 172.7 (CAg) 151.0 (C-2 py), 148.6 (C-6 py), 137.6 (C-4 py), 123.7(C-3 py), 123.5 (C-5 py), 54.7 (pyCH2), 50.4 (C-4/5
Sim). MS (ESI+):m/z 1249.1470 [(M ! BF4)
+, 0.1%], C45H48Ag3B2F8N12+ requires
1249.140330.
’ASSOCIATED CONTENT
bS Supporting Information. X-ray crystallographic data forthe complexes in CIF format; characterization of the compounds,including NMR, mass, and optical spectra; complete X-raystructural characterization, including thermal ellipsoid plots;
and tables of bond distances and angles. This material is availablefree of charge via the Internet at http://pubs.acs.org.
’AUTHOR INFORMATION
Corresponding Author*E-mail: [email protected].
’ACKNOWLEDGMENT
This material is based upon work supported by the NationalScience Foundation under Grant No. CHE-0549902.
’REFERENCES(1) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991,
113, 361.(2) John, A.; Ghosh, P. Dalton Trans. 2010, 7183.(3) K!uhl, O. Chem. Soc. Rev. 2007, 36, 592.(4) Douthwaite, R. E. Coord. Chem. Rev. 2007, 251, 702.(5) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978.(6) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.(7) Díez-Gonz"alez, S.; Stevens, E. D.; Scott, N. M.; Petersen, J. L.;
Nolan, S. P. Chem.—Eur. J. 2008, 14, 158.(8) Díez-Gonz"alez, S.; Nolan, S. P. Angew. Chem., Int. Ed. 2008,
47, 8881.(9) Ellul, C. E.; Reed, G.; Mahon, M. F.; Pascu, S. I.; Whittlesey,
M. K. Organometallics 2010, 29, 4097.(10) Lin, I. J. B.; Vasam, C. S. Comments Inorg. Chem. 2004,
25, 75.(11) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251, 642.(12) Kascatan-Nebioglu, A.; Panzner, M. J.; Tessier, C. A.; Cannon,
C. L.; Youngs, W. J. Coord. Chem. Rev. 2007, 251, 884.(13) Tiekink, E. R. T.; Kang, J.-G.Coord. Chem. Rev. 2009, 253, 1627.(14) Gimeno, M. C.; Laguna, A. Chem. Soc. Rev. 2008, 37, 1952.(15) Yam, V.W.-W.; Cheng, E. C.-C.Chem. Soc. Rev. 2008, 37, 1806.(16) Fern"andez, E. J.; Laguna, A.; L"opez-de-Luzuriaga, J. M. Dalton
Trans. 2007, 1969.(17) Balch, A. L. Gold Bull. 2004, 37, 45.(18) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2008, 37, 1931.(19) Pyykk!o, P. Inorg. Chim. Acta 2005, 358, 4113.(20) Pyykk!o, P. Angew. Chem., Int. Ed. 2004, 43, 4412.(21) Hermann, H. L.; Boche, G.; Schwerdtfeger, P. Chem.—Eur. J.
2001, 7, 5333.(22) Carvajal, M. A.; Alvarez, S.; Novoa, J. J. Chem.—Eur. J. 2004,
10, 2117.(23) O’Grady, E.; Kaltsoyannis, N. Phys. Chem. Chem. Phys. 2004,
6, 680.(24) Poblet, J.-M.; B"enard, M. Chem. Commun. 1998, 1179.(25) Fern"andez, E. J.; L"opez-de-Luzuriaga, J. M.; Monge, M.;
Rodríguez, M. A.; Crespo, O.; Gimeno, M. C.; Laguna, A.; Jones,P. G. Inorg. Chem. 1998, 37, 6002.
(26) Catalano, V. J.; Malwitz, M. A. Inorg. Chem. 2003, 42, 5483.(27) Liu, L.-g.; Bassett, W. A. J. Appl. Phys. 1973, 44, 1475.(28) Catalano, V. J.; Malwitz, M. A.; Etogo, A. O. Inorg. Chem. 2004,
43, 5714.(29) Garrison, J. C.; Tessier, C. A.; Youngs,W. J. J. Organomet. Chem.
2005, 690, 6008.(30) Kim, G. Y.; Jung, H. J.; Park, G.; Lee, D.-H. Bull. Korean Chem.
Soc. 2010, 31, 1739.(31) Zhang, X.; Gu, S.; Xia, Q.; Chen, W. J. Organomet. Chem. 2009,
694, 2359.(32) Catalano, V. J.; Moore, A. L. Inorg. Chem. 2005, 44, 6558.(33) Strasser, C. E.; Catalano, V. J. J. Am. Chem. Soc. 2010,
132, 10009.(34) Lin, J. C. Y.; Huang, R. T. W.; Lee, C. S.; Bhattacharyya, A.;
Hwang, W. S.; Lin, I. J. B. Chem. Rev. 2009, 109, 3561.
L dx.doi.org/10.1021/ic201053t |Inorg. Chem. XXXX, XXX, 000–000
Inorganic Chemistry ARTICLE
(35) Chen,W.; Liu, B. Faming Zhuanli Shenqing Gongkai Shuomingshu2010, CN101787542.(36) Liu, B.; Xia, Q.; Chen,W. Angew. Chem., Int. Ed. 2009, 48, 5513.(37) Ye, J.; Jin, S.; Chen, W.; Qiu, H. Inorg. Chem. Commun. 2008,
11, 404.(38) Xi, Z.; Zhang, X.; Chen, W.; Fu, S.; Wang, D. Organometallics
2007, 26, 6636.(39) Liu, B.; Chen, W.; Jin, S. Organometallics 2007, 26, 3660.(40) Garrison, J. C.; Simons, R. S.; Tessier, C. A.; Youngs, W. J.
J. Organomet. Chem. 2003, 673, 1.(41) Zhang, X.; Xi, Z.; Liu, A.; Chen, W. Organometallics 2008,
27, 4401.(42) Zhou, Y.; Chen, W. Organometallics 2007, 26, 2742.(43) Yang, C.; Elbjeirami, O.; Gamage, C. S. P.; Dias, H. V. R.;
Omary, M. A. Chem. Commun. 2011, 47, 7434.(44) Rawashdeh-Omary, M. A.; Rashdan, M. D.; Dharanipathi, S.;
Elbjeirami, O.; Ramesh, P.; Dias, H. V. R. Chem. Commun. 2011,47, 1160.(45) Burini, A.; Mohamed, A. A.; Fackler, J. P., Jr. Comments Inorg.
Chem. 2003, 24, 253.(46) Yang, G.; Raptis, R. G. Inorg. Chem. 2003, 42, 261.(47) Masciocchi, N.; Moret, M.; Cairati, P.; Sironi, A.; Ardizzoia,
G. A.; La Monica, G. J. Am. Chem. Soc. 1994, 116, 7668.(48) Dias, H. V. R.; Diyabalanage, H. V. K.; Rawashdeh-Omary, M. A.;
Franzman, M. A.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 12072.(49) Dias, H. V. R.; Diyabalanage, H. V. K.; Eldabaja, M. G.;
Elbjeirami, O.; Rawashdeh-Omary, M. A.; Omary, M. A. J. Am. Chem.Soc. 2005, 127, 7489.(50) Grimes, T.; Omary, M. A.; Dias, H. V. R.; Cundari, T. R. J. Phys.
Chem. A 2006, 110, 5823.(51) Magill, A. M.; McGuinness, D. S.; Cavell, K. J.; Britovsek,
G. J. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; White, A. H.;Skelton, B. W. J. Organomet. Chem. 2001, 617!618, 546.(52) Ng, C.; Sabat, M.; Fraser, C. L. Inorg. Chem. 1999, 38, 5545.(53) Vieille-Petit, L.; Luan, X.; Mariz, R.; Blumentritt, S.; Linden, A.;
Dorta, R. Eur. J. Inorg. Chem. 2009, 1861.(54) Sabiah, S.; Lee, C.-S.; Hwang, W.-S.; Lin, I. J. B.Organometallics
2010, 29, 290.(55) Martin, N. H.; Allan, N. W.; Moore, K. D.; Vo, L. J. Mol. Struct.:
THEOCHEM 1998, 454, 161.(56) Ray, M.; Ghosh, D.; Shirin, Z.; Mukherjee, R. Inorg. Chem.
1997, 36, 3568.(57) Garces, F. O.; King, K. A.; Watts, R. J. Inorg. Chem. 1988,
27, 3464.(58) Effendy; Marchetti, F.; Pettinari, C.; Skelton, B. W.; White,
A. H. Inorg. Chim. Acta 2007, 360, 1424.(59) Di Nicola, C.; Effendy; Marchetti, F.; Pettinari, C.; Skelton,
B. W.; White, A. H. Inorg. Chim. Acta 2007, 360, 1433.(60) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.; Cavallo,
L.; Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 2485.(61) Winkelmann, O. H.; Riekstins, A.; Nolan, S. P.; Navarro, O.
Organometallics 2009, 28, 5809.(62) Liu, B.; Zhang, Y.; Xu, D.; Chen, W. Chem. Commun. 2011,
47, 2883.(63) Meyer, E. M.; Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. Organometallics 1989, 8, 1067.(64) Sundararaman, A.; Lalancette, R. A.; Zakharov, L. N.; Rheingold,
A. L.; J!akle, F. Organometallics 2003, 22, 3526.(65) Kang, H. C.; Do, Y.; Knobler, C. B.; Hawthorne, M. F. J. Am.
Chem. Soc. 1987, 109, 6530.(66) Yam, V. W.-W.; Fung, W. K.-M.; Cheung, K.-K. Chem. Com-
mun. 1997, 963.(67) Yam, V. W.-W.; Lo, K. K.-W.; Wong, K. M.-C. J. Organomet.
Chem. 1999, 578, 3.(68) Yam, V. W.-W.; Lam, C.-H.; Cheung, K.-K. Inorg. Chim. Acta
2001, 316, 19.(69) Yam, V. W.-W.; Lo, W.-Y.; Lam, C.-H.; Fung, W. K.-M.; Wong,
K. M.-C.; Lau, V. C.-Y.; Zhu, N. Coord. Chem. Rev. 2003, 245, 39.
(70) Hu, B.; Gahungu, G.; Zhang, J. J. Phys. Chem. A 2007, 111, 4965.(71) Yam, V. W.-W.; Wong, K. M.-C.; Hung, L.-L.; Zhu, N. Angew.
Chem., Int. Ed. 2005, 44, 3107–3110.(72) Liao, S.-H.; Shiu, J.-R.; Liu, S.-W.; Yeh, S.-J.; Chen, Y.-H.; Chen,
C.-T.; Chow, T. J.; Wu, C.-I. J. Am. Chem. Soc. 2009, 131, 763.(73) Rausch, A. F.; Thompson, M. E.; Yersin, H. J. Phys. Chem. A
2009, 113, 5927.(74) Chang, C.-F.; Cheng, Y.-M.; Chi, Y.; Chiu, Y.-C.; Lin, C.-C.;
Lee, G.-H.; Chou, P.-T.; Chen, C.-C.; Chang, C.-H.; Wu, C.-C. Angew.Chem., Int. Ed. 2008, 47, 4542.
(75) Yang, C.-H.; Cheng, Y.-M.; Chi, Y.; Hsu, C.-J.; Fang, F.-C.;Wong, K.-T.; Chou, P.-T.; Chang, C.-H.; Tsai, M.-H; Wu, C.-C. Angew.Chem., Int. Ed. 2007, 46, 2418.
(76) Bhansali, U. S.; Polikarpov, E.; Swensen, J. S.; Chen, W.-H.; Jia,H.; Gaspar, D. J.; Gnade, B. E.; Padmaperuma, A. B.; Omary, M. A. Appl.Phys. Lett. 2009, 95, 233304.
(77) Develay, S.; Blackburn, O.; Thompson, A. L.; Williams, J. A. G.Inorg. Chem. 2008, 47, 11129.
(78) Fern"andez, E. J.; Laguna, A.; L"opez-de-Luzuriaga, J. M. A.;Olmos, M. E.; P"erez, J. Chem. Commun. 2003, 1760.
(79) Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson, F.Organometallics 1993, 12, 3405.
(80) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972.(81) Bildstein, B.; Malaun, M.; Kopacka, H.; Wurst, K.; Mitterb!ock,
M.; Ongania, K.-H.; Opromolla, G.; Zanello, P. Organometallics 1999,18, 4325.
(82) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton, B. W.;White, A. H. Dalton Trans. 2004, 3756.
(83) Mato-Iglesias, M.; Roca-Sabio, A.; P"alink"as, Z.; Esteban-G"omez, D.; Platas-Iglesias, C.; T"oth, E".; de Blas, A.; Rodríguez-Blas,T. Inorg. Chem. 2008, 47, 7840.
(84) Zeng, X.; Coqui#ere, D.; Alenda, A.; Garrier, E; Prang"e, T.; Li, Y.;Reinaud, O.; Jabin, I. Chem.—Eur. J. 2006, 12, 6393.
(85) SAINT: Program for data reduction, version 7.68A; Bruker AXS:Madison, WI, 2009.
(86) Sheldrick, G. M. SHELXTL: Structure Determination SoftwareSuite, version 6.10; Bruker AXS: Madison, WI, 2001.
(87) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.